geez...that's some plumbing scheme. Can you add some arrows to it to see which holes are in and which are out? I like it - I'm trying to do something similar with my new tank, albeit without drilling into the back of the tank (glass!). I'm trying to do it by fitting the
PVC piping down the back of the tank and having kind of a vertical spray bar as part of my return. The other returns are over the top of the tank (spider like). It looks kind of similar to yours, but not as solid.
Can't wait to see it up and running!
